Semiconductor substrates are widely used in manufacturing various devices that operate based on the unique electromagnetic properties of semiconductor materials. In many cases, the semiconductor substrates have a monocrystalline, or single-crystal, morphology. Crystalline silicon substrates may be conventionally obtained by sawing a plate from an ingot or boule of single crystal silicon grown using the Czochralski or floating zone process. The process of sawing the substrate produces a waste stream of powdered silicon, known as the kerf, which is the pulverized remains of a portion of the ingot the thickness of the saw blade. The powdered silicon is typically recycled into a new ingot, but the kerf makes up a significant percentage of the ingot, and therefore increases the cost of each individual plate obtained from the ingot.
Crystalline silicon substrates may also be obtained conventionally by growing an epitaxial layer onto a single crystal template substrate using a CVD process. The epitaxial layer is then cleaved from the template substrate by peeling or water sawing. Devices may be formed on the substrate before or after cleaving from the template substrate. Cleaving may be facilitated by forming pores in the template substrate prior to growing the epitaxial layer thereon, or by implanting ions at a selected depth to form a cleave seam. “Handle” substrates are frequently bonded to the epitaxial layer to facilitate handling after cleaving.
Conventional epitaxy is a slow process. A substrate, such as the template substrate referred to above, is disposed in a CVD chamber and heated to a processing temperature. A precursor gas mixture is provided to the chamber, and a surface of the template substrate is exposed to the gas. A layer grows on the template substrate atom by atom until a desired thickness is reached. Growing a monocrystalline substrate to a reasonable thickness, such as 500 μm, can take hours since growth rates for monocrystalline materials are limited. Liquid phase epitaxy may be practiced under very stringent conditions, with morphological results strongly dependent on maintaining tight control of the deposition interface. Solid phase epitaxy may also be used to create monocrystalline layers, but such processes usually require a great deal of energy to recrystallize polycrystalline or amorphous materials.
New methods and apparatus are needed to make monocrystalline and/or epitaxial semiconductor substrates at high rates.